{"id":4511,"date":"2019-06-24T12:55:16","date_gmt":"2019-06-24T12:55:16","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/5-1-case-study-genes-and-inheritance\/"},"modified":"2023-11-30T17:55:49","modified_gmt":"2023-11-30T17:55:49","slug":"5-1-case-study-genes-and-inheritance","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/5-1-case-study-genes-and-inheritance\/","title":{"raw":"5.1\u00a0Case Study: Genes and Inheritance","rendered":"5.1\u00a0Case Study: Genes and Inheritance"},"content":{"raw":" \r\n
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Case Study: Cancer in the Family<\/h1>\r\n<\/div>\r\n\r\n[caption id=\"attachment_2094\" align=\"alignleft\" width=\"430\"]\"Image Figure 5.1.1 Family tree - three generations.<\/em>[\/caption]\r\n\r\nPeople tend to carry similar traits to their biological parents, as illustrated by the family tree. Beyond just appearance, you can also inherit traits from your parents that you can\u2019t<\/em>\u00a0see.\r\n\r\nRebecca becomes very aware of this fact when she visits her new doctor for a physical exam. Her doctor asks several questions about her family medical history, including whether Rebecca has or had relatives with cancer. Rebecca tells her that her grandmother, aunt, and uncle \u2014 who have all passed away \u2014 had cancer. They all had breast cancer, including her uncle, and her aunt\u00a0also\u00a0had ovarian cancer. Her doctor asks how old they were when they were diagnosed with cancer. Rebecca is not sure exactly, but she knows that her grandmother was fairly young at the time, probably in her forties.\r\n\r\nRebecca\u2019s doctor explains that while the vast majority of cancers are not due to inherited factors, a cluster of cancers within a family may indicate that there are mutations in certain genes that increase the risk of getting certain types of cancer, particularly breast and ovarian cancer. Some signs that cancers may be due to these genetic factors are present in Rebecca\u2019s family, such as cancer with an early age of onset (e.g., breast cancer before age 50), breast cancer in men, and breast cancer and ovarian cancer within the same person or family.\r\n\r\nBased on her family medical history, Rebecca\u2019s doctor recommends that she see a genetic counselor, because these professionals can help determine whether the high incidence of cancers in her family could be due to inherited mutations in their genes. If so, they can test Rebecca to find out whether she has the particular variations of these genes that would increase her risk of getting cancer.\r\n\r\nWhen Rebecca sees the genetic counselor, he asks how her grandmother, aunt, and uncle with cancer are related to her. She says that these relatives are all on her mother\u2019s side \u2014 they are her mother\u2019s mother and siblings. The genetic counselor records this information in the form of a specific type of family tree, called a pedigree, indicating which relatives had which type of cancer, and how they are related to each other and to Rebecca.\r\n\r\nHe also asks her ethnicity. Rebecca says that her family on both sides are Ashkenazi Jews (Jews whose ancestors came from central and eastern Europe). \u201cBut what does that have to do with anything?\u201d she asks. The counselor tells Rebecca that mutations in two tumor-suppressor genes called BRCA1<\/a> and BRCA2<\/a>, located on chromosome 17 and 13, respectively, are particularly prevalent in people of Ashkenazi<\/a> Jewish descent and greatly increase the risk of getting cancer. About one in 40 Ashkenazi Jewish people have one of these mutations, compared to about one in 800 in the general population. Her ethnicity, along with the types of cancer, age of onset, and the specific relationships between her family members who had cancer, indicate to the counselor that she is a good candidate for genetic testing for the presence of these mutations.\r\n\r\n[caption id=\"attachment_2096\" align=\"alignright\" width=\"429\"]\"In Figure 5.1.2 Rebecca is not sure if she wants to know if she is at an increased risk of breast and ovarian cancer.<\/em>[\/caption]\r\n\r\nRebecca says that her 72-year-old mother never had cancer, nor had many other relatives on that side of the family. How could the cancers be genetic? The genetic counselor explains that the mutations in the BRCA1 and BRCA2 genes, while dominant, are not inherited by everyone<\/em> in a family. Also, even people with mutations in these genes do not necessarily get cancer \u2014 the mutations simply increase their risk of getting cancer. For instance, 55 to 65 per cent of women with a harmful mutation in the BRCA1 gene will get breast cancer before age 70, compared to 12 per cent of women in the general population who will get breast cancer sometime over the course of their lives.\r\n\r\nRebecca is not sure she wants to know whether she has a higher risk of cancer. The genetic counselor understands her apprehension, but explains that if she knows that she has harmful mutations in either of these genes, her doctor will screen her for cancer more often and at earlier ages. Therefore, any cancers she may develop are likely to be caught earlier when they are often much more treatable. Rebecca decides to go through with the testing, which involves taking a blood sample, and nervously waits for her results.\r\n
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Chapter Overview: Genetics<\/h1>\r\n<\/header>\r\n
\r\n\r\nAt the end of this chapter, you will find out Rebecca\u2019s test results. By then, you will have learned how traits are inherited from parents to offspring through genes, and how mutations in genes such as BRCA1 and BRCA2 can be passed down and cause disease. Specifically, you will learn about:\r\n